PROJECT 6 : Pharmacologic Inhibitors of Cellular Kinases and Signal Transduction Chronic lymphocytic leukemia (CLL) is currently initially treated with chemoimmunotherapy (CIT). Despite this advance, virtually all patients receiving CIT relapse and ultimately die from their disease. Recent identification of targets central to the biology of B-cell transformation provides an opportunity to set a new treatment paradigm in CLL, as has been done in chronic myeloid leukemia. In this regard, we are investigating clinically active kinase inhibitors that target cyclin-dependent kinases (CDK; flavopihdol and SCH727965) and phosphoinositide 3-kinase delta (PlSK-delta; CAL-101). Flavopiridol, SCH727965, and CAL-101 each have demonstrated signficant clinical activity in patients with relapsed and refractory CLL. The mechanisms by which each ofthese agents kill CLL cells and interfere with microenvironmental protection, as well as pathways by which resistance develops, are uncertain. Through detailed mechanistic interrogation we will confirm and extend our strong prelimitiary data. In conjunction, we will also perform translational studies accompanying CRC phase l/ll trials with each agent. Specific Aim 1: To perform mechanistic studies of flavopiridol and SCH727965 to study: a) The contribution of ER stress to cell death promoted by these agents, b) The contribution of autophagy to CDK inhibitor drug resistance; c) The influence of microenvironment on promoting resistance to CDK inhibitors in CLL cells and strategies to overcome these with novel targeted agents, and d) performance of pharmacodynamic studies with completed and planned CDK inhibitor clinical trials in the CRC. Specific Aim 2: To interrogate the PI3K-delta pathway with particular focus on: 1) Identification ofthe mechanism by which CAL-101 promotes direct cytotoxicity toward CLL cells; 2) Relevance of external signals antagonized by CAL-101 in the microenvironment to the survival of CLL cells; 3) Pre-clinical testing of PI3K-delta inhibitors in the TCLI mouse model of CLL to further validate optimal combination studies with this agent, and 4) performance of pharmacodynamic studies in concert with the planned CAL-101 clinical trials in the CRC.